Patent GB-1372221-A (GB)
Title: Compositions for making moulded refractory articles
IPC: B22C1/22
Filed: 1971-12-02
Abstract: 1372221 Refractory mixtures PRECISION METALSMITHS Inc 2 Dec 1971 [2 Dec 1970 22 Feb 1971] 56011/71 Heading C1J [Also in Division C3] A refractory mixture consists of (a) a comminuted refractory material as the major component; (b) a sublimable binder which is a solid at 20 C., can be melted and resolidified, and has a vapour pressure of at least 0À1 mm. of Hg at its triple point and (c) at least 0À8% by wt. based on the total weight of the mixture, of a second binder which is a solid at 20 C., is miscible with the sublimable binder when the latter is in the liquid state, can be hardened to impart strength to articles formed from the mixture, has a vapour pressure lower than that of the sublimable binder so that the second binder will hold articles moulded from the mixture intact during sublimation of the sublimable binder, which second binder comprises from 4À5 to 100%, by wt. based on the weight of the second binder, of ethyl cellulose, the ethyl cellulose being present in an amount of at least 0À5% by wt. of the total weight of the mixture. The binders are organic compounds which can be melted to the liquid state on heating and resolidified on cooling. The sublimable binder may have a triple point temperature above 20 C., a boiling point not greater than 250 C., or a vapour pressure of at least 0À1 mm. Hg at 20 C. and a boiling point not greater than 200 C. The mixture may comprise 10 to 35% by wt. sublimable binder and 0À8 to 11% by wt. of the second binder. Refractory articles, e.g. a mould component, may be made by injection moulding the article from the mixture, subliming the sublimable binder to produce a porous structure, and either firing to sinter the refractory material or at least partially impregnating the pore structure of the moulded article with an impregnating agent consisting essentially of a refractory binder in a carrier liquid, and hardening the impregnant. Alternatively the mixture may be cast, poured, transfer moulded or extruded. The sublimable binder may be p-dichlorobenzene, urethane, acetamide, naphthalene, benzoic acid, phthalic anhydride, camphor, anthracene, pchlorobenzaldehyde, 1-bromo-4-chlorobenzene, p-dimethoxy and p-dibutoxy-benzene and crotonic acid. In addition to ethyl cellulose, the second binder may contain resins and polymers, e.g. polymerized rosins, hydrogenated rosin esters, petroleum hydrocarbon resins, coumarone-indene, ester gums, polyterpene, polystyrene, polyvinyl acetate, polyvinyl alcohol, chlorine polyphenyl resins, gilsonite, abietic acid, shellac, and silicones. Examples of impregnant are hydrolysed alkyl silicates such as ethyl or isopropyl silicate, silica sols or dispersions, inorganic silicates such as lithium polysilicate, sodium and potassium silicate, quaternary ammonium silicates, aluminium acid phosphate, mono aluminium phosphate, aluminium formate, zirconium acetate, ammonium zirconyl carbonate. Examples of refractories are fused and crystalline silica, zircon, zirconia, alumina, calcium zirconate, aluminium silicates, tricalcium phosphate and nepheline syenite.